Strip form feeds from indent passed to dedent_to (#24381)

dylwil3 · web-flow · commit 7fdb55618994 · 2026-04-02T20:14:59.000-05:00
When adjusting "simple" indentation in the formation of edits, we attempt to dedent manually rather than deferring to LibCST. To do so we must provide a desired indentation, in the form of a string. We often grab this from source code by slicing the text in a range beginning at the start of a line. In Python, the start of a line may contain form feeds but these do not contribute to the indentation. In this PR, we strip the provided indentation of its leading form feeds in order to get the correct indentation amount for use in `dedent_to`. This avoids the introduction of a syntax error in the edit [`adjust_indentation`](https://github.com/astral-sh/ruff/blob/1f430e68af6e627569776dfbcd03b98ac7c29eb6/crates/ruff_linter/src/fix/edits.rs#L429). Note: We could try to stay closer to the user's intent by prepending the form feed prefix of the provided indentation _everywhere_ in the resulting edit, but that seems a little unwieldy and this is a bit of an edge case anyway. Closes #24373
diff --git a/crates/ruff_linter/resources/test/fixtures/ruff/RUF072.py b/crates/ruff_linter/resources/test/fixtures/ruff/RUF072.py
@@ -176,4 +176,12 @@
     1
     2
 finally:
-    pass
+    pass
+
+
+# Regression test for https://github.com/astral-sh/ruff/issues/24373
+# (`try` is preceded by a form feed below)
+try:
+    1
+finally:
+    pass
diff --git a/crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__preview__RUF072_RUF072.py.snap b/crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__preview__RUF072_RUF072.py.snap
@@ -349,3 +349,25 @@ help: Remove the `finally` clause
     -     pass
 175 + 1
 176 + 2
+177 |
+178 |
+179 | # Regression test for https://github.com/astral-sh/ruff/issues/24373
+
+RUF072 [*] Empty `finally` clause
+   --> RUF072.py:186:1
+    |
+184 |   try:
+185 |       1
+186 | / finally:
+187 | |     pass
+    | |________^
+    |
+help: Remove the `finally` clause
+181 |
+182 | # Regression test for https://github.com/astral-sh/ruff/issues/24373
+183 | # (`try` is preceded by a form feed below)
+    - try:
+    -     1
+    - finally:
+    -     pass
+184 + 1
diff --git a/crates/ruff_python_trivia/src/textwrap.rs b/crates/ruff_python_trivia/src/textwrap.rs
@@ -203,6 +203,11 @@ pub fn dedent(text: &str) -> Cow<'_, str> {
 /// # Panics
 /// If the first line is indented by less than the provided indent.
 pub fn dedent_to(text: &str, indent: &str) -> Option<String> {
+    // The caller may provide an `indent` from source code by taking
+    // a range of text beginning with the start of a line. In Python,
+    // while a line may begin with form feeds, these do not contribute
+    // to the indentation. So we strip those here.
+    let indent = indent.trim_start_matches('\x0C');
     // Look at the indentation of the first non-empty line, to determine the "baseline" indentation.
     let mut first_comment_indent = None;
     let existing_indent_len = text
@@ -753,4 +758,18 @@ mod tests {
         ].join("");
         assert_eq!(dedent_to(&x, ""), Some(y));
     }
+
+    #[test]
+    #[rustfmt::skip]
+    fn dedent_to_ignores_leading_form_feeds_in_provided_indentation() {
+        let x = [
+            "  1",
+            "  2",
+        ].join("\n");
+        let y = [
+            "1",
+            "2",
+        ].join("\n");
+        assert_eq!(dedent_to(&x, "\x0C\x0C"), Some(y));
+    }
 }

Original file line number	Diff line number	Diff line change
`@@ -176,4 +176,12 @@`
`176`	`176`	`1`
`177`	`177`	`2`
`178`	`178`	`finally:`
`179`		`- pass`
	`179`	`+ pass`
	`180`	`+`
	`181`	`+`
	`182`	`+# Regression test for https://github.com/astral-sh/ruff/issues/24373`
	`183`	+# (`try` is preceded by a form feed below)
	`184`	`+try:`
	`185`	`+ 1`
	`186`	`+finally:`
	`187`	`+ pass`